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Ha showing secondary image

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Need some help with this please. Just started narrowband imaging with Baader filters and I'm seeing some very strange effects that I can't explain. Anyone seen this before and how do I get rid of it? Basically it looks like the primary, secondary and spider are showing up on the images.

Here is a 200s sub in Ha (2x2) and an associated flat. I get seomthing similar for OIII too - but not SII.
Telescope is 250mm f4.8 newt with an MPCC, Atik 460EX and Baader filters.

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It is an unstacked sub but you can see the same pattern in both the sub and the flat. All subs in Ha and OIII have this. It was reasonably dark last night (or as good as it gets here on the edge of Edinburgh) so don't think it was against light.

Both images seriously stretched to show the issue.

Thanks

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It is an unstacked sub but you can see the same pattern in both the sub and the flat. All subs in Ha and OIII have this. It was reasonably dark last night (or as good as it gets here on the edge of Edinburgh) so don't think it was against light.

Both images seriously stretched to show the issue.

Thanks

Hmm... Sometimes, where I am, I'll get momentary headlights which are very annoying. However, that wouldn't explain your flat. Were all your subs the same? Has it happened before? If not has something changed?

Louise

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Flats and subs all show the same in Ha and OIII. SII doesn't show these that I can see.
The only thing that's changed is that this is the first real full narrowband image I've done - so a big change really

Wondering if it's out of focus reflections from the MPCC to the Baader filters?

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One other possibility is the acrylic over the EL panel I use for flats being reflective?

Suppose I need to try and change everything to see what works.

That wouldn't explain the uncalibrated subs showing the problem. Did you buy the filters new? If you don't get the problem without the filters, it must be something to do with them, I think. I'm sure someone on here will know what's causing the problem.

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It looks like image that can be seen when you look at eyepiece with naked eye.

Strange thing is that it is "focused" at that particular distance.

Reflection of flat panel can actually be the issue here coupled with CC. It cannot be problem on its own - many people have reflective light boxes, but in your case something is creating focus at that exact spot.

I have two suggestions that you can try:

1. Put a piece of thin paper over your flat panel to dim it, but point is to make it non reflective rather than dim the light

2. Move your flat panel a bit further (as you probably can't get it closer) to aperture opening. Just to see what sort of effect this will give you.

Try combination of the two above as well.

Interestingly SII does not produce that? I find this very strange, because if it were due to flat panel - it would show up in SII being so close to Ha, don't think that there would be such dramatic difference in reflectivity or anything.

Another thing that you can try is to figure out what reflective surface is causing this, you can use this distance calculator for that:

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You Ha sub of horse head is showing this artifact and flat box was not nowhere near when you took that. It's reflection and one fairly distant because the size of it.

Now that I'm thinking about it - nothing special in the artifact except the size - and that means reflective surface is very far away. What sort of CC are you using? I suspect that it's one with large back focus and not standard 55mm one, although it depends on speed of scope - faster scopes throw larger defocus image for same reflection distance.

All reflection artifacts look like that - but they are smaller and secondary is usually not seen due to star in center, but spikes are always present - defocus image represents aperture - so spikes and secondary will both be seen in it. You can get the same image by defocusing enough bright star.

You Ha sub of horse head is showing this artifact and flat box was not nowhere near when you took that. It's reflection and one fairly distant because the size of it.

Now that I'm thinking about it - nothing special in the artifact except the size - and that means reflective surface is very far away. What sort of CC are you using? I suspect that it's one with large back focus and not standard 55mm one, although it depends on speed of scope - faster scopes throw larger defocus image for same reflection distance.

All reflection artifacts look like that - but they are smaller and secondary is usually not seen due to star in center, but spikes are always present - defocus image represents aperture - so spikes and secondary will both be seen in it. You can get the same image by defocusing enough bright star.

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Are the spacers that you use to get the correct back-focus distance before or after the FW?

I had a really odd internal reflection when I got my new Chroma NB filters and the only way I could deal with it was by putting the spacers between the FW and camera, rather than the recommended FW closest to the sensor.

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First check is that MPCC distance is wrong. I've adjusted it (not totally correct yet but I'll sort that) and at first glance the pattern has gone! May have been chance that the position I chose just happened to produce a very nicely focused image of the spider and secondary!

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Well I've finally decided that it is caused by the MPCC and the Baader filters together - even at the correct spacing there's still some effect.

The really weird thing is that my images look far better without the MPCC. I only used it because it was necessary with my 8 inch Newtonian, but this 10 inch seems not to need it at all - and it certainly gets rid of the the horrible reflections / artifacts.

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Well I've finally decided that it is caused by the MPCC and the Baader filters together - even at the correct spacing there's still some effect.

The really weird thing is that my images look far better without the MPCC. I only used it because it was necessary with my 8 inch Newtonian, but this 10 inch seems not to need it at all - and it certainly gets rid of the the horrible reflections / artifacts.

Thanks again for everyone's help and suggestions.

Mark

Ah yes, I see your sensor is quite small so it looks like you can get away without a flattener. APS-c size, - not so much!
Glad you got it going ok.